Exotic wild animals and fractious, aggressive pets are often presented in cages for treatment by veterinarians. Handling these animals in a manner that is both safe to the veterinarian and humane for the animal may be impossible without anesthesia. It is important to minimize struggling and excessive fright to the animal since prolonged excitation can disturb the circulatory and metabolic state of the animal and induce a degree of shock. However, attempts to anesthetize a struggling wild animal or fractious pet presents safety problems in addition to enhancing the likelihood of an abnormal response. These points are particularly pertinent to the restraint and anesthesia of wild animals.
By definition tranquilizers produce psychological calming of anxiety without physiological depression or clouding of consciousness. However, when tranquilizers are used to produce manageability, high doses are usually necessary which may result in ataxia, variable response to stimulation and cardiorespiratory depression. Cardiovascular depression may be severe and, if followed by a general anesthetic, the combination may lead to severe hypotension.
Tranquilizers do not exert hypnotic or analgesic affects. Increasing the dose does not produce greater sedation, even though the psychological depressant affects are magnified.
The psychological state of the animal prior to administration of tranquilizers may markedly affect the degree of sedation achieved. Animals that are vicious, intractable and in a state of excitation may not become manageable, except with very high (incapacitating) doses, therefore it is often preferred to treat these animals with an anesthetic instead of tranquilizers.
Dissociative anesthetics produce a state of chemical restraint and anesthesia characterized by a form of muscle rigidity and an apparent dissociation of the mind from the external environment. The eyes remain open; various reflexes, including the blinking reflex remain intact. Adequate respiration is normally maintained, an increase in heart rate and blood pressure frequently occurs. While the widest use of dissociative anesthetic agents is probably with primates and felines, they have also been used in most other mammalian species as well as birds and reptiles.
Currently, these dissociative anesthetics and tranquilizers are administered via a dart delivered from a blowgun or syringe pole. Problems associated with darts are numerous. The dart must enter muscle tissue and fully discharge to deliver the calculated dose of drugs. Occasionally darts miss the animal entirely or do not discharge the drug into muscle tissue. Inadvertent movement of the animal may allow the dart to hit the animal's eye or other organ that may produce damage and harm. With injectable drugs it is difficult to estimate the amount of drug to use. An overdose may produce death and an under dose may produce more agitation and excitement. Some animals, especially primates that have been darted in the past are very apprehensive when they know that they are to be darted again. The time from darting to restraint of the patient is very unpredictable. Darting devices used by unskilled operators can produce more damage than benefits.
Inhalant anesthetics delivered in sufficient quantity over a short period of time give a relatively rapid onset and rapid recovery after the inhalation anesthetic is discontinued. They can be administered with a high degree of controllability over anesthetic depth and duration through the manipulation of drug dose, rate of vaporization, and cessation of administration when the desired effect is produced on the animal. To date, however, specialized, expensive vaporizers and oxygen equipment has been required to use inhalant anesthetics. These devices are very expensive and delivery of anesthetic to large cages and chambers is very prolonged before effects on the animal are seen.
Monitoring the dosage of inhalant anesthetic is important. Differences in anesthetic solubility determine the speed with which gas concentration builds up in the arterial blood. As highly soluble gases require more time to build up a significant concentration in the blood, they result in a more prolonged induction and recovery. The reverse is true of the highly insoluble gases which are therefore more controllable as their blood concentration can be rapidly changed; however, for this reason they are more hazardous and require quantitative methods to govern their delivery in safe concentrations.
Currently, inhalant anesthetics can be administered by means of a simple nose cone for the performance of short procedures or via a mask or endotrachial tube connected to a vaporizer. Numerous apparati have been devised for these purposes, but none of these can be effectively used to treat the excited or vicious animal before removing it from its cage. The current way to deliver anesthetics to cages is to flow oxygen through an expensive precision vaporizer. This method consumes large volumes of oxygen and volatile liquid anesthetics. For animals in large chambers, a prolonged period of time is necessary to induce an anesthetic state. This method is not adaptable to use in the field except with a lot of heavy, complex, and expensive equipment.
Accordingly, what is needed in the art is a simple, inexpensive, transportable device and method to safely anesthetize wild or otherwise vicious animals while they are in their transport cages.